For example, in order to open or close a toilet seat or a toilet lid with respect to a Western style toilet bowl, a hinge device is provided between the toilet seat or the toilet lid and the Western style toilet bowl. The hinge device includes a cylindrical case, and a shaft body that is inserted into the case and can be rotated relative to the case. One of the case and the shaft body is fixed to the Western style toilet bowl, and the other thereof is fixed to the toilet seat or the toilet lid. When the toilet seat or the toilet lid is rapidly closed, loud sound or a large impact is generated. In order to prevent this, an annular region between the case and the shaft body is filled with viscous fluid that generates a damping force. The annular region is compartmentalized into a high-pressure chamber and a low-pressure chamber in a circumferential direction. An orifice, which narrows a flow passage of the viscous fluid flowing to the low-pressure chamber from the high-pressure chamber, is formed between the high-pressure chamber and the low-pressure chamber so as to be capable of resisting the rotation of the shaft body when the shaft body is rotated in one direction (for example, when the toilet seat or the toilet lid is rotated so as to be closed). When the toilet seat or the toilet lid is rotated so as to be closed, the orifice generates the damping force and softens the impact generated when the toilet seat or the toilet lid is closed (for example, see Patent Document 1).
The hinge device, which generates the damping force by using the orifice, has an advantage of being able to generate the damping force that corresponds to the magnitude of loading. On the other hand, when overloading (forced opening and closing and impulsive opening and closing except loading in normal use) is given, an internal pressure of the high-pressure chamber rises. For this reason, there is a concern that components such as the case and the shaft body are damaged. If the stiffness of the components is increased in order to cope with the overloading, cost is increased.
In order to prevent the damage to the components, the hinge device disclosed in Patent Document 1 is provided with an adjustment valve that releases the internal pressure of the high-pressure chamber. When the pressure in the high-pressure chamber 1 is a usual internal pressure, the adjustment valve 3 is seated on an impact releasing valve 4 due to a spring force of a coil spring 2 as shown in FIG. 16A. Accordingly, the high-pressure chamber 1 and the low-pressure chamber 5 are shut off. Meanwhile, when overloading is applied and the pressure in the high-pressure chamber 1 becomes excessively high pressure, the adjustment valve 3 moves downward against the spring force of the coil spring 2 and is separated from the impact releasing valve 4 as shown in FIG. 16B. Accordingly, the viscous fluid of the high-pressure chamber 1 flows to the low-pressure chamber 5 through the adjustment valve 3. Since the high-pressure chamber 1 is connected with the low-pressure chamber 5 and the internal pressure of the high-pressure chamber 1 decreases, it may be possible to prevent the components from being damaged.
Patent Document 1: Japanese Patent No. 3339802